Feline intraocular tumors may arise from transformation of lens epithelium

Feline ocular sarcomas are malignant intraocular neoplasms that are frequently associated with a history of ocular trauma. They usually present as fibrosarcomas, but some have both epithelial and mesenchymal features. The purpose of this study was to determine the cell of origin of a subset of feline intraocular sarcomas that display a mixed epithelial-mesenchymal phenotype, with elaboration of basement membrane-type matrix. We examined the morphology and histochemical and immunohistochemical phenotypes of nine feline intraocular sarcomas. Immunohistochemistry and in situ hybridization were performed to detect expression of crystallin alpha A. In addition, tumors were examined for expression of vimentin, cytokeratin, smooth muscle actin, desmin, melan A, neural cell adhesion molecule, S-100, glial fibrillary acidic protein, nerve growth factor receptor, and collagen type IV. Animals ranged from 7 to 17 years of age--no breed or sex predilection for tumor occurrence was present. Tumors were characterized by mixed epithelial and mesenchymal phenotypes, both of which elaborated basement membrane-type material and expressed vimentin highly. On the basis of collagen type IV and crystallin alpha A immunopositivity, we established that three of nine tumors were of lens epithelial origin. Expression of desmin and smooth muscle actin identified one tumor as a leiomyosarcoma. The remainder were undifferentiated sarcomas of myofibroblastic origin. This is the first report of lens epithelial neoplasia in clinical material from any species. The history and morphologic features of feline ocular sarcomas are reminiscent of feline vaccine-induced sarcomas. These tumors may share pathophysiologic similarities unique to this species.